Do you have a program that you normally use for CD burning? Most burning programs will take a FLAC (or just about any audio format) and convert it to the proper format as long as you set-up the program for an "audio CD". I use ImgBurn, (FREE!!!) and I always feed-in 44.1kHz/16-bit stereo WAV files.

It it was me, I'd make WAV files and use an audio editor to "manually" adjust the volumes. I mostly use GoldWave, but Audacity (FREE!!!) or any other audio editor can adjust volumes.

Or, WinAmp has a "WAV Out" option that will send the output to a WAV file. I assume it will apply ReplayGain (or any other "effects").

MP3Tag (FREE!!!!) can manually edit ReplayGain tags (and not just MP3 files). Click View -> Extended Tags. I assume foobar2000 can do it too, but I don't use foobar2000.

In foobar2000, you can right-click a selection and use the ReplayGain menu to scan the albums. You can use Shift-Right-Click to reveal the Edit ReplayGain Info menu (or edit Preferences (Ctrl-P)/Display/Context Menu/ReplayGain to choose to display that menu item by default).

You can edit a playlist and keep an eye on the properties when all are selected to see the total duration.

The Right-click Convert... menu includes a Write Audio CD... option. The dialogue box allows you to turn on ReplayGain Processing (and choose the type e.g Album Gain, Apply Gain), DSP Processing (e.g. Advanced Limiter to control high peaks while maintaining the desired volume level) and Dither (on or off) and Burn Gaplessly (on or off)

I think I will have to process the playlist first as it was created from the PC which just has the AAC copies, so I will need to write some sort of script to copy the original flacs before editing the RPG tags.